Related Applications
The entire disclosure of Japanese Patent Application No. H09-337770 filed on Nov. 20, 1997, including specification, claims, drawings, and summary, are incorporated h ere in by reference in its entirety.
1. Field of the Invention
The present invention relates to a chair having an automatic cyclically inclining seat. The invention relates, in detail, to an automatic cycle seat having adjustable cycles and adjustable inclinations which is driven mechanically to incline cyclically forward and backward and/or side-to-side. The seat is designed to enhance sitting posture mobility by continuously changing the hip-joint angle (angle between trunk and thighs), lumbosacral angle (promontory angle), and trunkal lateral flexion angle. The seat of this invention further diminishes the strain of muscles surrounding the pelvis as well as the dorsolumbar muscles. Finally, pain in the breech and femoral region and swelling in the inferior limbs is mitigated by displacing contact with the seat.
2. Description of the Prior Art
Various attempts have been made to improve the design of office chairs and thus eliminate problems, such as lower back pain, which arise from sitting for long periods of time in certain positions. However, no chair has been designed which can prevent pain in the breech and femoral regions or swelling of the inferior limbs which occurs after prolonged sitting. Numerous problems arise from prolonged sitting. For example, prolonged sitting may induce chronic contractions in the posture-sustaining muscles (e.g., elector spinae, iliopsoas, and leg muscles), resulting in muscle fatigue and circulatory disorders manifested b y lower back pain and inferior limb swelling. A prolonged sitting position can also block the nutritive diffusion into interspinal disks, resulting in interspinal disk disorder and lower back pain. The interspinal disks have no blood vessels and are metabolized by nutrition diffused from peripheral vessels. This diffusion is prompted by the changes in the internal pressure of the interspinal disks which result from changing postures. Finally, a prolonged sitting position generates pressure on the regions in contact with the seat (i.e., ischial tuberosities and the back of the thighs), which induces circulatory disorders, resulting in pain in breech and thighs as well as swelling of the inferior limbs. Various chairs with manually-inclining seats have been utilized, including the rocking chair, which inclines as a whole, as well as chairs which allow the seat alone to be inclined.
The rocking chair has been used principally for rest. It is inclined by pressing one's feet against the floor or by swinging the upper body. The rocking chair cannot, however, be adapted to different operations. Moreover, it inclines only in the sagittal direction, not in the lateral direction. Its inclining ranges may be roughly adjusted by the feet or by upper body movement, but it cannot be minutely adjusted. A standard rocking chair's inclining rate is as high as sixteen (16) degrees per 1.6 seconds (inclining frequency is one cycle per 1.6 seconds or 0.63 Hz) when inclined with the upper body movement alone. Such a rapid inclination causes the line of vision to be rapidly displaced, resulting in eye strain and other difficulties in continuing office operations. When posture-locking operations are involved, its inclination rate is lowered since it is manually inclined. Furthermore, the rocker cannot be equipped with casters and has difficulties in rotating or displacements.
A seat-inclining chair comprises a seat on an inclining axis beneath its center, and is mobile within a range of between -5.degree. (backward inclination) and +20.degree. (forward inclination). The seat is inclined by displaced breech position or trunkal flexion. Although the inclining center, range, and rate are adjustable, each cannot be minutely adjusted. Furthermore, the inclination direction is solely sagittal, not lateral, and the inclining mechanism undermines the stable seat support and thus increases muscle contraction. Such a seat is difficult to operate. Since the seat-inclining chair is manually operated, its inclination rate is lowered when increased posture-locking operations are involved.
There are numerous problems and shortcomings in the above-mentioned conventional inclining chairs. These problems include the following:
1. Preferable Seat Inclinations Vary Depending Upon Individual Operations-When general office operations such as writing, reading, or retrieving documents are involved, a seat which allows the individual to incline forward is preferred. However, during typing or computer operations, a relatively backward inclined posture is preferred. This difference in inclining posture results from the varied positions of the objects being used (i.e., the computer screen, book, etc.) with respect to the individual. For example, for typing or computer operations in which the typing paper or screen is not even with the desk but rather inclined toward the operator, a slightly backward inclined posture is preferred. Preferable postures, therefore, differ depending upon the operations or arrangements of the objects. To resolve this problem, it is necessary to ensure that the inclination of the inclining center (motor center for cyclic inclination) can be freely adjusted in reference to the flat seat position. The seat position determined by a set inclining center is hereinafter referred to as the set inclination reference position.
2. Seat Inclination Increases as Time Elapses--During general office operations, forward seat inclination increases as sitting time increases. Typically, the anterior inclination of a seat will increase from 8.5 degrees to 9.2 degrees during 48 minutes of sitting. To resolve this problem, the inclining center must be able to continuously shift from its initial inclination in reference to the flat seat position (initial set inclination reference position) through another set inclination (final set inclination reference position) after a specified duration.
3. Inclining Range and Inclining Frequency Increase as Sitting Time Elapses--In general office operations, the seat inclining range and frequency are increased as sitting time elapses. Inclinations of two degrees or more will increase on the average from 40 per hour to 88 per hour for 48 minutes, while those of less than two degrees on the average will increase from 514 per hour to 621 per hour for the same duration. These increases result from the operator's attempt to avoid strained postures and to mitigate resulting fatigue. To resolve this problem, an office chair must be equipped with a mechanism which can increase the inclining range and frequency proportionate to elapsed time.
4. Highly Constraining Operations Reduce Inclining Range and Inclining Frequency--Keying leads to reduced inclining range and inclining frequency when compared to other typical office operations. This reduction is due to the intensely constrained posture specific to keying. To resolve this problem, the office chair must be provided with an automatic inclining mechanism which is driven mechanically rather than manually.
5. Frequency of Recrossing Legs Increases as Sitting Time Elapses--To avoid continued pressure in the ischial region, some individuals continually recross their legs during work requiring sitting. When legs are crossed, the overlying leg is relieved of the compression that was built up previously in the ischial tuberosities. To resolve this continued pressure, an office chair must recline in the rightward and leftward directions.
6. Inclining Rate--Greater inclining rates require the line of vision and posture to be quickly adjusted which may cause eye strain or other difficulties in the individual. To resolve this problem, the inclining rate must be adequately controlled.
7. Seat Stability--Seat stability is essential for office work requiring precision. Manually inclining chairs lack this stability. To overcome this problem, a chair must be equipped with an automatic inclining mechanism wherein the mechanism is driven mechanically rather than manually.